The objective of the proposed investigation is to delineate the mechanism(s) whereby the src gene protein (pp60src) of the Rous sarcoma virus interacts with cellular components to induce both morphological and tumorgenic transformation. The studies will be performed with a mammalian cell line (Microtus agrestis, field vole) transformed by an avian oncornavirus. One of the interesting features of transformed vole cells is their ability to partially revert to the normal cell phenotype. Studies to date indicate that revertant vole cells: (1) exhibit all the growth properties of uninfected normal vole cells with the major exception that they are tumorgenic is nude mice; (2) contain the entire biologically functional viral genome including the viral gene (src) required for neoplastic transformation; and (3) express all of the viral genes including the transforming gene sequences as RNA at levels similar to transformed vole cells. Thus, the unique feature of the revertant vole cells is the expression of viral src gene induced tumorgenicity in the absence of viral induced in vitro transformation. Consequently, the transformed/revertant vole cell system may provide the experimental means to distinguish between those interactions of the src gene protein (pp60src) with host cell components that are responsible for tumorgenic and in vitro transformation. Studies are proposed (1) to quantitate the amount of pp60src present in both cell types; (2) to determine the activity of the pp60src associated protein kinase; (3) to perform rigorous structural analysis of revertant and transformed vole cell pp60src; (4) to determine the cellular localization of pp60src in both cell types; and (5) to identify the cellular components with which pp60src interacts.